This invention relates particularly to a solenoid type electromagnetic pump to be operated with intermittent d-c currents obtained by the half-wave rectification of a commercial alternating current power source.
In this type of electromagnetic pump device, strenuous improvements have been made for the prevention of "beat" during operation and also for the rapid stoppage of feeding of oil when stopped.
The beat in this kind of electromagnetic valve is in general originated from the chattering of a valve disposed particularly for controlling the feeding of oil and various countermeasures have been proposed so far. As typical countermeasures, various systems which are driven by currents such as A-C, full-wave rectified current and D-C, for example, have been in service, but each of them has both merits and demerits and therefore exhibits different performance in actual use. In more details, the prevention of beat during operation and the rapid stoppage of the valve when the power is disconnected are substantially antinomic in the case of the electromagnetic valve actuated by alternating current. For the electromagnetic valves driven by direct current or currents obtained by full-wave rectification, the beat may be appreciably reduced, but they are disadvantageous in that power source systems become rather complicated, that the breaking time or time interval from the disconnection of power to the stoppage of the valve becomes longer and that attraction force in a main magnetic circuit used for driving a plunger is decreased.
In addition, it is well known to those skilled in the art that the oil leak after the stoppage of pump is attributed to the time delay until the pump internal pressure or oil head pressure during the feeding through the action of leading-in or suction is diminished, when an oil storage tank is located at a higher or lower position than the place where the pump is installed. In short, in the case of the former, it results in the outflow due to leakage and the so-called after-loose, while for the latter it results in the after-loose. Such phenomena may become the cause of troubles such as the breaking-out of a fire and the occurrence of a nasty smell and a poisonous gas due to incomplete combustion or the explosion within a furnace, so that it has been desired for a long time that an electromagnetic pump which is safe in operation and also cheap in cost can be provided.
Besides, the chattering of the electromagnetic pump, which may be the main cause of noises, causes their surfaces of abutment to wear which in turn further increases its chattering, thus leading the pump to any damage or more leakage of oil at the time when the pump is stopped.